Poke a few holes in the skin of the uncut spaghetti squash with a fork. Place entire uncut squash in the microwave and microwave for 8-10 minutes on high to get skin pliable enough to cut.
Use a dish towel to remove the squash to your cutting board and cut from end to end in half.
Remove and discard seeds.
Place squash cut side down on a plate or platter and microwave on high for about 15 minutes, using five minute intervals. Once the squash is soft, invert and using a fork, pull and scrape the meat from the squash, finishing with a spoon to remove all flesh from shell. Discard the outer shell.
Toss with tomatoes and pesto and serve. (Note: If your pesto is too thick, add some additional olive oil to loosen it.)